Cough Syrups' Sweetness, Viscosity Drive Their Effectiveness

By Anne Harding

September 23, 2020

NEW YORK (Reuters Health) - Over-the-counter cough medicines help ease cough due to the common cold because they're sweet and viscous, not because they contain active ingredients like dextromethorphan and guaifenesin, according to a new review.

"The clinical trials that are out there don't support the effectiveness of these medicines, and really we've evolved back to cough medicines being more like food products," Dr. Ronald Eccles, an emeritus professor at Cardiff University in Wales, told Reuters Health in a phone interview. "What is important is the food color, flavor, the taste of the cough medicine, rather than the pharmacology."

Honey was the first cough medicine, and remains a popular remedy today, Dr. Eccles notes. "I think the key thing about honey is it's sweet and viscous, and any sweet syrup would provide the same benefit."

Dr. Eccles, a leading expert on the placebo effect in cough treatment, describes more than 100 excipients found in 60 OTC liquid cough medicines in his review, published in Lung. The article groups the additives into six categories: sweeteners, thickeners, flavors, colors, antimicrobials and buffers.

Liquid glucose, sucrose, saccharine sodium, liquid sugar and sorbitol were the most common sweeteners used in the cough medicines analyzed. Sweetness may help fight cough by promoting salivation and soothing the throat, Dr. Eccles notes, and sucrose has been shown to increase cough reflex threshold.

Glycerol and propylene glycol were the most frequently used thickeners, in 48 and 20 of the medicines tested, respectively. Menthol and levomenthol were the most common flavoring agents, found in 34 medicines, followed by anise oil and aniseed flavor, in 22; caramel, in 19; and capiscum tincture, in 13.

Benzoates and ethanol 96% were the most commonly used antimicrobials, found in 43 and 23 of medicines tested, respectively.

Dr. Eccles said he prefers cough medicines without active ingredients. "You can take them as often as you wish, whereas if you're going to take dextromethorphan, you're limited to taking it every four to six hours," he said. A simple sweet syrup can also be given to children and used during pregnancy, "and it will be as beneficial as any of the active cough medicines," he added.

Cough is the single most common reason patients in the U.S. go to the doctor, Dr. Peter Dicpinigaitis, a professor at Albert Einstein College of Medicine in New York City and editor-in-chief of Lung, told Reuters Health by phone.

Nevertheless, he noted, "most doctors don't know anything about over-the-counter cough and cold medicines." Dr. Eccles' report helps explain why cough medicines come in sweet syrup form, he added, and "offers some interesting background about some things that doctors are not typically taught in medical school or elsewhere."

SOURCE: Lung, online September 5, 2020.